I have tried to Privia PX 830 and was impressed. There are no dealers in my area that carry the Celviano series. However Costco has an amazing price on the AP 420, $799. I was always sort of leaning towards the 620 however for $799, its hard to beat this deal.
So my question is this. What is the main difference between the 620 and 420? And it it worth an extra $700? On paper, I see that the 620 has more tones and a bigger speaker and midi compatible. It also has a digital display. Again, are these fesatures worth almost twice the price? And further to that, the PX 830 and the AP 420 are the exact same price (with $300 off deal for the AP 420) What is the main point of difference between those 2? On paper, it looks like they are exactly the same except the obvious physical appearance.

Ap 420 and PX-830 appear to be the same piano except for the cabinets. Celvianos have the more traditional cabinets for those who want them to blend in with their home decore. They have the same features. The one downside is that both of these have no MIDI IN or OUT jacks, only USB MIDI. AP 620 has line in line out and MIDI IN OUT jacks and has a slightly more powerful amp at 30 watts. There are the 250 sounds and built in rhythms. The PX-330 is the same thing as the AP-620.

Galaxy thanks for that. For the price difference ($700) would you go for the 620 over the 420?

Well it depends on what you are looking for from the piano. The additional sounds and rhythms are a waste if you will not use them. Likewise, the MIDI IN and OUT jacks are not needed if you don't plan to do control other keyboards or connect sound modules and have more sounds available. You can connect to a computer through the USB Midi and use software for sounds.
Unless you need the fancy cabinet the PX-130 would give you the same features as the AP420/PX830 and the PX-330 would be the same as the AP 620. All depends on your needs as to which to buy. Have you played either of these. Don't make the mistake of buying without playing.

Get the least expensive model in the lineup. I use a $600 Williams Overture, the least expensive model in the Williams digital console line, and it's adequate for any playing, from jazz improvisation to big-time concertos.

I have the AP-220 and am very satisfied with it.

What are you going to do with the piano? First off, all the Casios have the same piano sounds and same key action. So if you just want to practice piano with headphone get the lowest cost model, the PX130. For that purpose nothing is gained by spending more money.

But maybe you have some other use in mind that requires use of MIDI ports or Line Out jack. Then buy a piano with that.

I think the way to buy a Casio is to start with the PX130 then move up the models if you need more features until you have just what you will actually use then stop at that model. The best values are at the lower end. The key is to know what you will use. So one model has 20 more sounds Will you actualy play a string bass sound? or if you get into music production would you use a software bass?

Don't send a lot on bigger speakers. If you need that, buy them later. You get much better quality with externals

But don't spend to much on any Casio. Once you to $1000 then you can jump up into the mid-range of other brands and there is a lot to be gained.

It depends whether you need them. :-)

I don't know the consoles as well as the portable models, but really, only you can decide if you would really enjoy the extra tones, or if you think you'll want to connect it to other MIDI equipment without having to use a computer. The digital display is largely related to the extra tones, since its biggest function is probably to let you see which of the hundreds of sounds are selected... not so much of an issue when there are far fewer sounds to choose from to begin with. The better speaker system is nice, but irrelevant if you're mostly playing through headphones. Also, if that ends up being the only thing really drawing you to the more expensive model, you might find you can buy an even better sound system for the difference in price between the two models.

On paper, the 420 and 830 look awfully similar apart from the cabinetry and the speakers.